The present invention relates to a process for chemically milling parts formed from a metallic material, in particular, a titanium alloy, and to a milling solution used to mill such parts.
Chemical milling of castings formed from titanium alloys such as Ti 6-2-4-2 (a titanium based alloy containing 6 wt % aluminum, 2 wt % tin, 4 wt % zirconium, 2 wt % molybdenum, and the balance essentially titanium) generally results in unacceptable intergranular attack which results in an approximate 10xc3x97debit in low cycle fatigue life and a corresponding decrease in high cycle fatigue capability. This impacts fatigue limited parts formed from chemically milled titanium alloys such as stator vanes and casings on jet engines.
Thus, there is a need for a process and a milling solution which allows desired metal removal without the occurrence of significant intergranular attack.
Accordingly, it is an object of the present invention to provide a chemical milling process for parts which avoids the occurrence of significant intergranular attack.
It is a further object of the present invention to provide an improved chemical milling solution for carrying out the aforementioned chemical milling process.
The foregoing objects are attained by the chemical milling process of the present invention and the novel chemical milling solution of the present invention.
In accordance with the present invention, a process for chemically milling a metallic part without causing significant intergranular attack broadly comprises the steps of: providing a milling solution containing nitric acid, hydrofluoric acid, dissolved titanium, a wetting agent, and water; maintaining the milling solution at a temperature in the range of from about 110xc2x0 F. to 130xc2x0 F.; and immersing said part formed from a titanium alloy in the milling solution for a time sufficient to mill a desired depth on at least one surface of the part.
In accordance with the present invention, a solution for chemically milling a metal part formed without causing significant intergranular attack is formed from nitric acid, hydrofluoric acid, dissolved titanium, a wetting agent, and the balance water.
Other details of the chemical milling process and the chemical milling solution of the present invention, as well as other objects and advantages attendant thereto, are set forth in the following detailed description and the accompanying drawings wherein like reference numerals depict like elements.